Fast synchronization scheduling apparatus and method for time slotted channel hopping in congested industrial wireless network environment

ABSTRACT

The fast synchronization scheduling apparatus includes: a radio frequency (RF) transmission and reception module configured to transmit and receive RF signals from nearby channels, a received signal strength indicator (RSSI) reception and storage module configured to receive RSSI values from the RF signals received from the RF transmission and reception module and store the received RSSI values, a channel sorting module configured to measure Channel Quality Estimation (CQE) values of the respective channels by putting the RSSI values of the respective channels received from the RSSI reception and storage module into a CQE formula and to sort the channels in order of highest CQE value (highest channel quality) based on the measured CQE values.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 15/770,743, filed onApr. 24, 2018, which is a national stage of PCT Application No.PCT/KR2017/013263 filed on Nov. 21, 2017. Furthermore, this applicationclaims the foreign priority benefit of Korean Application No.10-2016-0181340 filed on Dec. 28, 2016. The disclosures of these priorapplications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a Time Slotted Channel Hopping (TSCH)scheme, which is a Time Division Multiple Access (TDMA)-based MediumAccess Control (MAC) protocol, and more particularly, to a fastsynchronization scheduling apparatus and method for, on the basis ofcongestion of a network, an arrangement state of nodes, and a quality ofa communication channel, reducing a listening time of nodes that desireto join.

BACKGROUND ART

Today, the Internet of Things (IoT) is considered a technology that isthe most widely used in real life. In IoT, seamless data transmissionand energy efficiency are important, and thus a low power networktechnology, such as a wireless sensor network, plays a crucial role.Also, in industry, a technology referred to as the Industrial Internetof Things (IIoT) has emerged as a new trend.

In the early 2000s, significant development occurred on ISA100.11a,Wireless HART, and other wireless technology standards, which haveexpandability and efficiency, that were suitable for industrialenvironments with numerous restrictive requirements. WirelessHART is atechnology that has greatly improved the reliability and stability ofwireless communication technologies, and WirelessHART employs TimeSlotted Channel Hopping (TSCH) Media Access Control (MAC) protocol onthe basis of the IEEE 802.15.4 standard. In 2012, the TSCH MAC protocolused in WirelessHART was adopted as a standard technology by beingincluded in an IEEE 802.15.4e MAC amendment that improved on constraintsof the existing IEEE 802.15.4-2006 standard. The IEEE 802.15.4e standardbelongs to the license-free 2.4 GHz (Industrial Scientific and Medical)ISM band and is divided into 16 separate channels for use.

In the TSCH MAC protocol, nodes across a network are synchronized intime, enabling start times of slotframes to be matched and channelhopping information to be shared. The slotframe is repeated during anoperation time, and a single slotframe includes a plurality of timeslots. sleep, translate, and receive operations are performed for asingle time slot. Channel hopping is a technology for transmitting andreceiving data by varying the frequency used in each time slot, andwhich is provided to resolve problems associated with congestion.

Among steps of configuring the entire topology in the TSCH MAC protocol,there is a step of joining a synchronization for a networkconfiguration. New nodes desiring to join the network need to receive anadvertisement packet (ADV) that contains scheduling information that istransmitted by nodes that have already joined the network and requiredfor the synchronization.

In order to use scheduling technology and channel hopping technology,which operate in the TSCH MAC, the synchronization technology is theessential and important factor. A node to join a network does not knowscheduling information of the network until listening to the ADVmessage, and thus are limitlessly kept in a listening state. This lowersthe energy efficiency of small devices that operate on batteries,shortening the period of actual operation, which can cause seriousmaintenance problems.

In order to enhance the productivity efficiency in a basic industrialenvironment, wireless communication is widely used. Wireless dataexchanges for automation have been more frequently taking place. Most ofthe wireless communications used herein share a 2.4 GHz ISM band witheach other, and interference caused by human and equipment movement maylimitlessly extend a waiting state of a node that is listening in aparticular channel.

In order to meet the reliability and stability, which are the mostimportant characteristics in an industrial wireless network, there isneed for a faster and more flexible synchronization strategy accordingto channel status and change.

DISCLOSURE Technical Problem

The present invention is directed to providing a fast synchronizationscheduling apparatus and method capable of, on the basis of networkcongestion, an arrangement state of nodes, and a quality of acommunication channel, reducing a listening time of a node desiring tojoin.

The technical objectives of the present invention are not limited tothose disclosed above, and other objectives may become apparent to thoseof ordinary skill in the art on the basis of the following description.

Technical Solution

One aspect of the present invention provides a fast synchronizationscheduling apparatus for Time Slotted Channel Hopping (TSCH) in acongested industrial wireless network environment, the fastsynchronization scheduling apparatus including: a radio frequency (RF)transmission and reception module configured to transmit and receive RFsignals from nearby channels; a received signal strength indicator(RSSI) reception and storage module configured to receive RSSI valuesfrom the RF signals received from the RF transmission and receptionmodule and store the received RSSI values; a channel sorting moduleconfigured to measure Channel Quality Estimation (CQE) values of therespective channels by putting the RSSI values of the respectivechannels received from the RSSI reception and storage module 20 into aCQE formula, and sort the channels in order of highest CQE value(highest channel quality) based on the measured CQE values; and achannel setting and advertisement packet (ADV) reception moduleconfigured to receive an input of a channel having the highest CQE valuefrom the channel sorting module, set the channel, and start a listeningoperation to receive an ADV in the set channel.

The channel sorting module may use, as a method of measuring the CQEvalue (channel quality), a Channel Quality Estimation method based on areceived signal strength indicator (RSSI).

Another aspect of the present invention provides a fast synchronizationscheduling apparatus for TSCH in a congested industrial wireless networkenvironment, the fast synchronization scheduling apparatus including: aRF transmission and reception module configured to transmit and receiveRF signals from nearby channels; an information collector configured toreceive ADVs and RSSI values from the RF signals received from the RFtransmission and reception module and measure CQE values of therespective channels by putting the RSSI values of the respectivechannels into a CQE formula, and collect information about a number ofcoordinators and information about a good group; and an ADV packetgenerator and scheduler configured to deliver information about a numberof coordinators and a number of allocated ADV slots to a PAN coordinatoron the basis of the information about the number of the coordinators andthe information about the good group that are collected from theinformation collector, and upon receiving an answer, generate an ADVmessage and transmit the generated ADV message in a channel designatedfor each coordinator.

The information collector may include: a RSSI reception and storagemodule configured to receive the RSSI values from the RF signalsreceived from the RF transmission and reception module and store thereceived RSSI values; an ADV receiver configured to receive the ADVreceived from the RF transmission and reception module and identify anumber of other coordinators; a channel sorting module configured tomeasure CQE values of the respective channels by putting the RSSI valuesof the respective channels received from the RSSI reception and storagemodule into a CQE formula, and sort the channels in order of highest CQEvalue (highest channel quality) based on the measured CQE values; and analgorithm determiner configured to set a number of coordinators and agood group by using the ADV, the number of coordinators, and the CQEvalues that are identified from the ADV receiver and the channel sortingmodule, and select channels having a high CQE value.

The algorithm determiner may include: a channel selecting moduleconfigured to select, on the basis of a predetermined threshold value, achannel that is determined not to be congested among the channels sortedin order of highest CQE value by the channel sorting module; and a groupsetting module configured to set the number of coordinators and the goodgroup that are measured by the ADV receiver.

The ADV packet generator and scheduler may include: an ADV slotallocation requesting module configured to deliver information about thenumber of coordinators set by the algorithm determiner (240) and thenumber of the allocated ADV slots to the PAN coordinator; and an ADVinformation generating module configured to receive an answer from thePAN coordinator on the basis of the information delivered from the ADVslot allocation requesting module, generate an ADV message, and transmitthe generated ADV message in a designated channel.

The PAN coordinator may serve to perform, on an entire topology thataccords with allocation of ADV slots, scheduling on the basis of thegood group and the number of coordinators.

Another aspect of the present invention provides a fast synchronizationscheduling apparatus for TSCH in a congested industrial wireless networkenvironment, the fast synchronization scheduling apparatus including: aRF transmission and reception module configured to receive informationabout a good group and information about nearby coordinators withrespect to each coordinator from an information collector; a coordinatornumber calculating module configured to calculate a number ofcoordinators that share a communication distance with each coordinatoron the basis of the information received from the RF transmission andreception module; a good group channel calculating module configured tocalculate a number of channels classified as being part of the goodgroup on the basis of a CQE value included in the informationtransmitted from the RF transmission and reception module; and a controlmessage scheduling module configured to compare the number of channelsclassified as being part of the good group with the calculated number ofthe coordinators, allocate a channel to each coordinator on the basis ofa result of the comparison, and deliver information about the allocationto the RF transmission and reception module such that the informationabout the allocation is transmitted to each coordinator in a wirelessmanner.

Another aspect of the present invention provides a fast synchronizationscheduling method for TSCH in a congested industrial wireless networkenvironment, the fast synchronization scheduling method including stepsof: (a) measuring, by an RSSI reception and storage module, whether anRSSI value is found to exist in each of channels received from a RFtransmission and reception module; (b) detecting, by using the RFtransmission and reception module again, an RSSI value from each of thechannels when not even one RSSI value is found to exist among all thechannels as a result of the measurement; (c) detecting RSSI values fromtwo of all the channels when an RSSI value is found to exist in each ofthe channels as a result of the measurement; (d) measuring, by a channelsorting module, CQE values of the respective channels by putting theRSSI values of the respective channels into a CQE formula, and sortingthe channels in an order of the highest CQE value (a highest channelquality) based on the measured CQE values; (e) receiving, by a channelsetting and ADV reception module, an input of a channel that has beensorted by the channel sorting module and determined to have the highestCQE value, and starting a listening operation to receive an ADV in thechannel; and (f) selecting, when an ADV is not received by the time apredetermined number of slotframes have passed, a channel having thehighest CQE value again on the basis of CQE values collected by thattime, and returning to step (c) and proceeding with the subsequentsteps.

Another aspect of the present invention provides a fast synchronizationscheduling method for TSCH in a congested industrial wireless networkenvironment, the fast synchronization scheduling method including stepsof: (a) measuring, by a RSSI reception and storage module, whether anRSSI value is found to exist in each of channels received from a radiofrequency (RF) transmission and reception module 100; (b) detecting, byusing the RF transmission and reception module again, an RSSI value fromeach of the channels when not even one RSSI value is found to existamong all the channels as a result of the measurement; (c) detectingRSSI values from two of all the channels when an RSSI value is found toexist in each of the channels as a result of the measurement; (d)measuring, by a channel sorting module, CQE values of the respectivechannels by putting the received RSSI values of the respective channelsinto a CQE formula, and sorting the channels in an order of the highestCQE value (a highest channel quality) based on the measured CQE values;(e) searching for other coordinators in a surrounding area using an ADVreceived from an ADV receiver, setting a number of the foundcoordinators and a good group, and delivering information about channelshaving high CQE values to a PAN coordinator; and (f) when a time slotfor an ADV is allocated to each coordinator on the basis of theinformation delivered from the PAN coordinator and timeslot informationis received by the coordinator, generating an ADV message andtransmitting the generated ADV message in a designated channel duringthe time slot; and (g) selecting, when an ADV is not received by thetime a predetermined number of slotframes have passed, a channel havingthe highest CQE value again on the basis of CQE values collected by thattime, and returning to step (c) and proceeding with the subsequentsteps.

Step (f) may include: a first calculating step of calculating, by a goodgroup channel calculating module, a number of channels classified asbeing part of the good group on the basis of the CQE value when it isdetermined that the number of coordinators calculated by a coordinatornumber calculating module is one; a step of, when the number of channelsobtained as a result of the first calculating step is in a range of oneto three, allocating a number of channels (ADV slots) corresponding tothe number of channels obtained as the result of the first calculatingstep, and delivering information about the allocation to thecoordinator; a second calculating step of calculating, by the good groupchannel calculating module, a number of channels classified as beingpart of the good group on the basis of the CQE value when it isdetermined that the number of coordinators calculated by the coordinatornumber calculating module is two; a step of, when the number of channelsobtained as a result of the second calculating step is one, having thechannel (an ADV slot) be primarily allocated to a coordinator with alower numbered coordinator ID, and delivering information about theallocation to the coordinator; a step of, when the number of channelsobtained as a result of the second calculating step is two, having thechannels be respectively allocated to the two coordinators, anddelivering information about the allocation to the coordinators; a stepof, when the number of channels obtained as a result of the secondcalculating step is three, having two of the channels be allocated to acoordinator with a lower numbered coordinator ID, and having the oneremaining channel be allocated to the remaining coordinator, anddelivering information about the allocation to the coordinators; a stepof, when the number of coordinators calculated by the coordinator numbercalculating module is three or more, comparing the number ofcoordinators with the number of channels in the good group; a step of,when the number of the channels in the good group is smaller than thenumber of the coordinators as a result of the comparing, having thechannels in the good group be allocated to the coordinators in order oflowest numbered coordinator ID, and delivering information about theallocation to the coordinators; and a step of, when the number of thechannels in the good group is larger than or equal to the number of thecoordinators as the result of the comparing, having one channelallocated to one coordinator such that ADV messages are simultaneouslytransmitted in a plurality of channels, and delivering information aboutthe allocation to the coordinators.

When the number of channels obtained as a result of the firstcalculating step is four or more, the method may include allocatingthree channels as the three channels with the highest qualities (highestCQE values) among the four channels to the coordinator, and deliveringinformation about the allocation to the coordinator.

When the number of channels obtained as a result of the secondcalculating step is four or more, the method may include allocatingthree channels that are ranked as the three channels with the highestqualities (highest CQE values) among the four channels to thecoordinators and not using the remaining channel.

Advantageous Effects

The fast synchronization scheduling apparatus and method for TimeSlotted Channel Hopping (TSCH) in a congested industrial wirelessnetwork environment according to the present invention provide thefollowing advantageous effects.

First, since nodes desiring to join, according to channel quality, anetwork are able to switch channels, the present invention can beapplied to a congested or frequently changing industrial wirelessenvironment.

Second, since advertisement packets (ADVs) are more frequently sent in achannel in which nodes desiring to join are congested, nodes desiring tojoin a network can be more rapidly synchronized, thus enabling a fastertopology configuration and data exchange.

Third, since the present invention schedules ADV messages and operatesaccording to the number of nearby coordinators, congestion andinterference due to collision of ADV messages in the same channel can bereduced.

DESCRIPTION OF DRAWINGS

FIG. 1 is a slotframe for measuring a quality of a channel, which isproposed in the thesis.

FIG. 2 is a block diagram illustrating a configuration of a fastsynchronization scheduling apparatus for Time Slotted Channel Hopping(TSCH) applied in a node that desires to join a network in a congestedindustrial wireless network environment according to an embodiment ofthe present invention.

FIG. 3 is a flow chart showing a fast synchronization scheduling methodfor TSCH applied in a node that desires to join a network in a congestedindustrial wireless network environment according to an embodiment ofthe present invention.

FIG. 4 is a block diagram illustrating a configuration of a fastsynchronization scheduling apparatus for TSCH applied in a coordinatorin a congested industrial wireless network environment according to anembodiment of the present invention.

FIG. 5 is a flowchart showing a fast synchronization scheduling methodfor TSCH applied in a coordinator in a congested industrial wirelessnetwork environment according to an embodiment of the present invention.

FIG. 6 is a slotframe having an advertisement packet (ADV) slot addedthereto.

FIG. 7 is a block diagram illustrating a configuration of a fastsynchronization scheduling apparatus for TSCH applied in a Personal AreaNetwork (PAN) coordinator in a congested industrial wireless networkenvironment according to an embodiment of the present invention.

FIG. 8 is a flowchart showing a fast synchronization scheduling methodfor TSCH applied in a PAN coordinator in a congested industrial wirelessnetwork environment according to an embodiment of the present invention.

FIG. 9 is a flowchart showing a scheduling method for a fastsynchronization scheduling method for TSCH in a congested industrialwireless network environment, in which first to third embodiments of thepresent invention are applied.

MODES OF THE INVENTION

The above and other objects, features and advantages of the presentinvention will become more apparent to those of ordinary skill in theart by describing exemplary embodiments thereof in detail with referenceto the accompanying drawings.

Hereinafter, embodiments of a fast synchronization scheduling apparatusand method in a congested industrial wireless network environmentaccording to the present invention will be described with reference tothe accompanying drawings. However, the present invention is not limitedto such embodiments, and the present invention may be realized invarious forms. The embodiments to be described below are onlyembodiments provided to complete the disclosure of the present inventionand assist those skilled in the art to completely understand the scopeof the present invention. Therefore, the embodiments set forth hereinand illustrated in the configuration of the present invention are onlythe most preferred embodiments and are not representative of the fullthe technical spirit of the present invention, so it should beunderstood that they may be replaced with various equivalents andmodifications.

The present invention describes a fast synchronization apparatus andmethod using a channel quality measurement, in which, since an operationmethod in a node desiring to join a network, an operation method in acoordinator that transmits an advertisement packet (ADV) message, and anoperation method in a Personal Area Network (PAN) coordinator thatidentifies all pieces of information about coordinators and schedulesthe coordinators are different from each other, their respectiveoperation methods will be separately described.

First Embodiment

FIG. 2 is a block diagram illustrating a configuration of a fastsynchronization scheduling apparatus for Time Slotted Channel Hopping(TSCH applied in a node that desires to join a network in a congestedindustrial wireless network environment according to an embodiment ofthe present invention.

As shown in FIG. 2, the scheduling apparatus applied in a node desiringto join a network includes a radio frequency (RF) transmission andreception module 10 configured to transmit and receive RF signals fromnearby channels, a received signal strength indicator (RSSI) receptionand storage module 20 configured to receive RSSI values from the RFsignals received from the RF transmission and reception module 10 andstore the received RSSI values, a channel sorting module 30 configuredto measure Channel Quality Estimation (CQE) values of the respectivechannels by putting the RSSI values of the respective channels receivedfrom the RSSI reception and storage module 20 into a CQE formula ofEquation 1 as shown below and to sort the channels in order of highestCQE value (that is, highest channel quality) based on the measured CQEvalues, and a channel setting and ADV reception module 40 configured toreceive an input of a channel having the highest CQE value from thechannel sorting module 30, set the channel, and start a listeningoperation to receive an ADV in the set channel.

In this case, the channel sorting module 30 uses a Channel QualityEstimation method based on RSSI as a method of measuring a CQE value (achannel quality).

FIG. 1 is a slotframe for measuring a quality of a channel, which isproposed in the thesis, in which an RSSI value of a channel is measuredin a slot NF in the rear side of the slotframe, and a channel qualityvalue is shared between coordinators by using a slot RPT in a front sideof the slotframe, allowing the channel quality to be the same over theentire topology.

Equation 1 is a formula that is used for evaluation of a channelquality, and c is a number of a channel, NE[c] is a current RSSI valueof the channel, and QE[c]_(k-1) is a channel quality that is finallycalculated and stored. The first QE[c]_(k-1) has a value of NE[c] as itis, and after that, QE[c]_(k-1) and NE[c] are subject to correctionusing an appropriate weight value.

$\begin{matrix}{{{QE}\lbrack c\rbrack}_{k} = \left\{ {{{\begin{matrix}{{NF}\lbrack c\rbrack} & {{{if}\mspace{14mu} k} = 0} \\{{\alpha\;{{QE}\lbrack c\rbrack}_{k - 1}} + {\left( {1 - \alpha} \right){{NF}\lbrack c\rbrack}_{k}}} & {{{if}\mspace{14mu} k} \in \left\lbrack {1,\infty} \right)}\end{matrix}c} \in \left\lbrack {11,26} \right\rbrack},{\alpha \in \left\lbrack {0,1} \right\rbrack}} \right.} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Hereinafter, a fast synchronization scheduling method for TSCH appliedin a node that desires to join a network in a congested industrialwireless network environment having the above configuration according tothe present invention will be described.

FIG. 3 is a flow chart showing a fast synchronization scheduling methodfor TSCH applied in a node that desires to join a network in a congestedindustrial wireless network environment according to an embodiment ofthe present invention.

Referring to FIG. 3, first, the RSSI reception and storage module 20measures whether an RSSI value is found to exist in each channel(channel number 11 to channel number 26) received by the RF transmissionand reception module 10 (S10).

Then, when not even one RSSI value is found to exist among all thechannels as a result of the measurement in Operation S10, the RFtransmission and reception module 10 detects an RSSI value again fromeach of the channels (S20). In addition, RSSI values are detected fromtwo of all the channels when an RSSI value is found to exist in each ofthe channels as a result of the measurement in Operation S10 (S30).

Then, the channel sorting module 30 measures CQE values of therespective channels by putting the RSSI values of the respectivechannels into a CQE formula of Equation 1, and sorts the channels inorder of highest CQE value (that is, highest channel quality) based onthe measured CQE values (S40).

The channel setting and ADV reception module 40 receives an input of achannel that is sorted by the channel sorting module 30 and determinedto have the highest CQE value, and starts a listening operation toreceive an ADV in the channel (S50). When an ADV is not received by thetime four slotframes have passed, a channel having the highest CQE valueis selected again on the basis of CQE values collected by that time, andthe operation 30 are repeated. (S60).

Second Embodiment

FIG. 4 is a block diagram illustrating a configuration of a fastsynchronization scheduling apparatus for TSCH applied in a coordinatorin a congested industrial wireless network environment according to anembodiment of the present invention.

As shown in FIG. 4, the scheduling apparatus applied in a coordinatorincludes a radio frequency (RF) transmission and reception module 100configured to transmit and receive RF signals from nearby channels; aninformation collector 200 configured to receive ADVs and RSSI valuesfrom the RF signals received from the RF transmission and receptionmodule 100, measure Channel Quality Estimation (CQE) values of therespective channels by putting the RSSI values into the CQE formula ofEquation 1, and collect information about the number of coordinators andinformation about a good group; and an ADV packet generator andscheduler 300 configured to deliver information about the number ofcoordinators and the number of allocated ADV slots to a PAN coordinator400 on the basis of the information about the number of the coordinatorsand the information about the good group collected from the informationcollector 200, and upon receiving an answer, to generate an ADV messageand transmit the generated ADV message in a channel designated for eachcoordinator.

In this case, the information collector 200 includes an RSSI receptionand storage module 210 configured to receive the RSSI values from the RFsignals received from the RF transmission and reception module 100 andstore the received RSSI values, an ADV receiver 220 configured toreceive the ADV received from the RF transmission and reception module100 and identify the number of other coordinators, a channel sortingmodule 230 configured to measure CQE values of the respective channelsby putting the RSSI values of the respective channels received from theRSSI reception and storage module 210 into the CQE formula of Equation 1and to sort the channels in order of highest CQE value (that is, highestchannel quality) based on the measured CQE values, and an algorithmdeterminer 240 configured to set the number of coordinators and a goodgroup by using the ADV, the number of the coordinators, and the CQEvalues that are identified from the ADV receiver 220 and the channelsorting module 230 and to select channels having high CQE values.

The algorithm determiner 240 includes a channel selecting module 241configured to select a channel that is determined not to be congested,on the basis of a value of −70 bBm, among the channels sorted in orderof highest CQE value by the channel sorting module 230, and a groupsetting module 242 configured to set the number of coordinators and thegood group that are measured by the ADV receiver 220.

The ADV packet generator and scheduler 300 includes an ADV slotallocation requesting module 310 configured to deliver information aboutthe number of coordinators set by the algorithm determiner 240 and thenumber of the allocated ADV slots, which are set by the algorithmdeterminer 240, to the PAN coordinator 400, and an ADV informationgenerating module 320 configured to receive an answer from the PANcoordinator 400 on the basis of the information delivered from the ADVslot allocation requesting module 310, generate an ADV message, andtransmit the generated ADV message in a designated channel.

FIG. 6 is a slotframe having an ADV slot added thereto. The ADVinformation generating module 320 respectively transmits ADV messages inthe channels, which have been allocated by the PAN coordinator, intimeslots that are not used for Tx/Rx, on the basis of the slotframe.

In this case, the PAN coordinator 400 serves to perform, on the entiretopology that accord with allocation of ADV slots, scheduling on thebasis of the good group and the number of coordinators.

Hereinafter, a fast synchronization scheduling method for TSCH appliedin a coordinator in a congested industrial wireless network environmenthaving the above configuration according to the present invention willbe described.

FIG. 5 is a flowchart showing a fast synchronization scheduling methodfor TSCH applied in a coordinator in a congested industrial wirelessnetwork environment according to an embodiment of the present invention.

Referring to FIG. 5, first, the RSSI reception and storage module 210measures whether an RSSI value is found to exist in each channel(channel number 11 to channel number 26) received by the RF transmissionand reception module 100 (S100).

Then, when not even one RSSI value is found to exist among all thechannels as a result of the measurement in Operation S100, the RFtransmission and reception module 100 detects an RSSI value again fromeach of the channels (S200). In addition, RSSI values are detected fromtwo of all the channels when an RSSI value is found to exist in each ofthe channels as a result of the measurement in S100 (S300).

Then, the channel sorting module 230 measures CQE values of therespective channels by putting the received RSSI values of therespective channels into the CQE formula of Equation 1, and sorts thechannels in order of highest CQE value (that is, highest channelquality) based on the measured CQE values (S400).

Whether other coordinators are located in a surrounding area is searchedfor using an ADV received from the ADV receiver 220 (S500), the numberof the found coordinators and a good group are set, and informationabout channels having high CQE values is delivered to the PANcoordinator 400 (S600).

When a time slot for an ADV is allocated to each coordinator on thebasis of the information delivered from the PAN coordinator 400 (S700)and timeslot information is received by the coordinator (S800), an ADVmessage is generated and the generated ADV is transmitted in adesignated channel during the time slot (S900). Operation S700 will bedescribed in detail with reference to FIG. 8.

Then, when an ADV is not received by the time four slotframes havepassed, a channel having the highest CQE value is selected again on thebasis of CQE values collected by that time, and the method proceeds withthe operation S400 is repeated.

Third Embodiment

FIG. 7 is a block diagram illustrating a configuration of a fastsynchronization scheduling apparatus for TSCH applied in a PANcoordinator in a congested industrial wireless network environmentaccording to an embodiment of the present invention.

As shown in FIG. 7, the fast synchronization scheduling apparatus forTSCH applied in a PAN coordinator includes a RF transmission andreception module 410 configured to receive information about a goodgroup and information about nearby coordinators with respect to eachcoordinator from an information collector 200, a coordinator numbercalculating module 420 configured to calculate the number ofcoordinators that share a communication distance with each coordinatoron the basis of the information received from the RF transmission andreception module 410, a good group channel calculating module 430configured to calculate the number of channels classified as being partof the good group on the basis of a CQE value included in theinformation transmitted from the RF transmission and reception module410, and a control message scheduling module 440 configured to comparethe number of channels classified as being part of the good group withthe calculated number of the coordinators, allocate a channel to eachcoordinator on the basis of a result of the comparison, and deliverinformation about the allocation to the RF transmission and receptionmodule 410 such that the information about the allocation is transmittedto each coordinator.

Hereinafter, a fast synchronization scheduling method for TSCH appliedin a PAN coordinator in a congested industrial wireless networkenvironment having the above configuration according to the presentinvention will be described.

FIG. 8 is a flowchart showing a fast synchronization scheduling methodfor TSCH applied in a PAN coordinator in a congested industrial wirelessnetwork environment according to an embodiment of the present invention.

Referring to FIG. 8, when it is determined that the number ofcoordinators calculated by the coordinator number calculating module 420is one (S701), the good group channel calculating module 430 calculatesthe number of channels classified as being part of a good group on thebasis of the CQE value (first calculation) (S702).

When the number of channels obtained as a result of the firstcalculation is in the range of one to three, channels (ADV slots) areallocated in a number corresponding to the number of channels obtainedas the result of the first calculation (S703, S704, S705), andinformation about the allocation is delivered to the coordinator (S714).In this case, when the number of channels obtained as a result of thefirst calculating is four or more, three channels that are ranked as thethree channels with the highest qualities, (that is, highest CQE values)among the four channels are allocated to the coordinator, andinformation about the allocation is delivered to the coordinator. Thus,a single coordinator is able to transmit an ADV message in differentchannels according to the situation.

Then, when it is determined that the number of coordinators calculatedby the coordinator number calculating module 420 is two (S706), the goodgroup channel calculating module 430 calculates the number of channelsclassified as being part of a good group on the basis of the CQE value(second calculation) (S707).

When the number of channels obtained as a result of the secondcalculation is one, the channel (an ADV slot) is allocated to acoordinator with a lower numbered coordinator ID (S708), and informationabout the allocation is delivered to the coordinator (S714). In thiscase, since coordinator IDs are assigned to coordinators in the orderthat they joined the network, there are no duplicate ID numbers, andpreferably, a coordinator joining earlier is given a channel before acoordinator joining later. The following description is illustrated asallocating channels in order of lowest coordinator ID. However, theallocating of channels in order of lowest coordinator ID is merely anexample, and the present invention is not limited thereto.

When the number of channels obtained as a result of the secondcalculating step is two, the channels are respectively allocated to thetwo coordinators (S709), and information about the allocation isdelivered to the coordinators (S714).

When the number of channels obtained as a result of the secondcalculating step is three, two of the channels are allocated to acoordinator with a lower numbered coordinator ID, the one remainingchannel is allocated to the remaining coordinator (S710), andinformation about the allocation is delivered to the coordinators(S714). When the calculated number of channels is four or more, threechannels that are ranked the three channels with the highest qualities(highest CQE values) among the four channels are allocated to thecoordinator in the same manner as the above, and the remaining channelis not used.

Finally, when it is determined that the number of coordinatorscalculated by the coordinator number calculating module 420 is three ormore, the number of coordinators is compared with the number of channelsin the good group (S711).

As a result of the comparison in Operation S711, when the number of thechannels in the good group is smaller than the number of thecoordinators, the channels in the good group are allocated to thecoordinators in order of lowest numbered coordinator ID (S712), andinformation about the allocation is delivered to the coordinators(S714).

As a result of the comparison in Operation S711, when the number of thechannels in the good group is larger than or equal to the number of thecoordinators, one channel is allocated to one coordinator such that ADVmessages are simultaneously transmitted in a plurality of channels(S713), and information about the allocation is delivered to thecoordinators (S714).

FIG. 9 is a flowchart showing a scheduling method for a fastsynchronization scheduling method for TSCH in a congested industrialwireless network environment, in which first to third embodiments of thepresent invention are applied.

Referring to FIG. 9, the following description first assumes that thePAN coordinator 400, two coordinators (a first coordinator (ID:1) and asecond coordinator (ID:2)), and one node desire to join.

In this case, channels number 14, number 20, and number 26 have beensubject to a change in quality, and are ranked in the order of thechannel number 20, the channel number 14, and the channel number 26 onthe basis of highest channel quality. In this case, the node desiring tojoin listens to an ADV message in the channel number 20, which has thehighest channel quality.

The coordinators 300 a and 300 b deliver information about the qualitiesof the channels that they measured by themselves and information aboutnearby coordinators to the PAN coordinator 400, and are assignedchannels. For reference, assuming the above described, the firstcoordinator 300 a has an ID with a number lower than that of the secondcoordinator 300 b, such that the first coordinator 300 a is assigned thehigher ranked two channels having good quality.

With changes circumstance, the channels are subject to changes inquality, and are differently ranked in the order of the channel number26, the channel number 15, and the channel number 23. Accordingly, thenode desiring to join listens to an ADV in the channel number 26, whichhas the highest quality, and the coordinators 300 a and 300 b deliverinformation about the qualities of the channels that they measured bythemselves and information about nearby coordinators to the PANcoordinator 400, and are assigned channels according to the algorithm.

As shown in FIG. 9, the first coordinator 300 a is assigned the channelnumber 26 and the channel number 15, and the second coordinator 300 b isassigned the channel number 23.

Accordingly, the first and second coordinators 300 a and 300 b send ADVmessages in the respective channels assigned thereto, and the nodehaving received the ADV message joins the network.

Although the present invention has been particularly described withreference to exemplary embodiments, it should be understood by those ofskilled in the art that the embodiments disclosed above should beconsidered in a descriptive sense only and not for purposes oflimitation. In addition, it should be understood that variousembodiments are possible within the scope of the following claims.Therefore, the scope of the invention is defined not by the detaileddescription of the invention but by the appended claims, and encompassesall modifications and equivalents that fall within the scope of theappended claims and will be construed as being included in the presentinvention.

INDUSTRIAL APPLICABILITY

The present invention relates to a Time Slotted Channel Hopping (TSCH),which is a Time Division Multiple Access (TDMA)-based Medium AccessControl (MAC) protocol, and more particularly, to a fast synchronizationscheduling apparatus and method for, on the basis of congestion of anetwork, an arrangement state of nodes, and a quality of a communicationchannel, reducing a listening time of a node that desires to join.

What is claimed is:
 1. A fast synchronization scheduling method for TimeSlotted Channel Hopping (TSCH) in a congested industrial wirelessnetwork environment, the fast synchronization scheduling methodcomprising steps of: (a) measuring, whether an RSSI value is found toexist in each of channels; (b) in response to no RSSI value being foundto exist among all the channels as a result of the measurement in thestep (a), repeating the step (a); (c) detecting RSSI values from two ofall the channels when an RSSI value is found to exist in each of thechannels as a result of the measurement; (d) measuring, Channel QualityEstimation (CQE) values of the respective channels by putting thereceived RSSI values of the respective channels into a CQE formula, andsorting the channels in order of highest CQE value (a highest channelquality) based on the measured CQE values; (e) searching forcoordinators in a surrounding area using an advertisement packet (ADV)received from an ADV receiver, setting a number of the foundcoordinators and a good group, and delivering information about channelshaving high CQE values to a Personal Area Network (PAN) coordinator; (f)generating, when a time slot for an ADV is allocated to each coordinatoron the basis of the information delivered from the PAN coordinator andtimeslot information is received by the coordinator, an ADV message andtransmitting the generated ADV message in a designated channel duringthe time slot; and (g) selecting, when an ADV is not received by thetime a predetermined number of slotframes have passed, a channel havingthe highest CQE value again on the basis of CQE values collected by thattime, and returning to step (c) and proceeding with the subsequentsteps.
 2. The fast synchronization scheduling method of claim 1, whereinstep (f) comprises: calculating, a number of channels classified asbeing part of the good group on the basis of the CQE value, andcalculating a number of coordinators, wherein when the number ofcoordinators is one and when the number of channels is in a range of oneto three, allocating a number of channels (ADV slots) corresponding tothe number of channels, and delivering information about the allocationto the one coordinator, wherein when the number of coordinators is twoand when the number of channels is one, having the one channel (an ADVslot) be primarily allocated to a coordinator with a lower numberedcoordinator ID, and delivering information about the allocation to thecoordinator, wherein when the number of coordinators is two and when thenumber of channels is two, having the two channels be respectivelyallocated to the two coordinators, and delivering information about theallocation to the two coordinators, wherein when the number ofcoordinators is two and when the number of channels is three, having twoof the three channels be allocated to a coordinator with a lowernumbered coordinator ID, having the one remaining channel be allocatedto the remaining coordinator, and delivering information about theallocation to the three coordinators, wherein when the number ofcoordinators is three or more, comparing the number of coordinators withthe number of channels in the good group, wherein when the number ofcoordinators is three or more and when the number of the channels in thegood group is smaller than the number of the coordinators as a result ofthe comparing, having the channels in the good group be allocated to thecoordinators in order of lowest numbered coordinator ID, and deliveringinformation about the allocation to the coordinators, and wherein whenthe number of coordinators is three or more and when the number of thechannels in the good group is larger than or equal to the number of thecoordinators as the result of the comparing, having one channel beallocated to one coordinator such that ADV messages are simultaneouslytransmitted in a plurality of channels, and delivering information aboutthe allocation to the coordinators.
 3. The fast synchronizationscheduling method of claim 2, wherein when the number of coordinators isone and when the number of channels is four or more, further comprisingallocating three channels that are ranked as the three channels with thehighest qualities (highest CQE values) among the four channels to thecoordinator, and delivering information about the allocation to thecoordinator.
 4. The fast synchronization scheduling method of claim 2,wherein when the number of coordinators is two and when the number ofchannels is four or more, further comprising allocating three channelsthat are ranked as the three channels with the highest qualities(highest CQE values) among the four channels to the coordinators and notusing the remaining channel.